The present invention relates to digital data and file storage technologies, and more particularly to file storage technologies, such as NAS (Network Attached Storage), suitable for storing files safely over a network.
One example of storing files over a network is NAS. NAS, which is a storage (an external storage device) directly connected to a network such as a LAN (Local Area Network), comprises storage management software, a NAS operating system, a graphical user interface, and various types of hardware (processor, memory, storage interface, network interface, and so on).
The technologies implemented by those components allow a NAS unit (NAS server) to function on a network as an independent file server through which files are shared and, at the same time, allow a client to do operation as if access was made to a conventional file server.
However, a conventional NAS server does not have a function to prove the existence time and the non-alterability of stored data for a long time. Therefore, when it is desired to prove the data existence time and the non-alterability of data for a long time, the NAS user must take some guarantee measures in advance before storing data in NAS.
Taking such guarantee measures requires an additional cost because a special device is required. This increases a load on general NAS users.